Spampinato S, Canossa M, Campana G, Carboni L, Bachetti T
Department of Pharmacology, University of Bologna, Italy.
Endocrinology. 1995 Apr;136(4):1589-94. doi: 10.1210/endo.136.4.7895668.
Prodynorphin (Prodyn)-derived peptides are synthesized in a subset of gonadotrope cells and released concomitantly with LH and FSH, and their levels in the rat adenohypophysis are influenced by the gonadal steroid environment. In several hormonal systems, factors that affect peptide levels may modulate the transcription of messenger RNA (mRNA) encoding for the target gene. Therefore, the present study was designed to investigate the effects of gonadal ablation and estrogen replacement on changes in steady state levels of anterior pituitary Prodyn mRNA and on the transcription rate in the adult female rat. The antiestrogen tamoxifen was employed for further exploring the relationships between estrogens and dynorphin (dyn)-related peptides. Adopting a solution hybridization-ribonuclease protection assay, steady state levels of Prodyn mRNA doubled in 2-week ovariectomized (OVX) rats, in parallel with a 3-fold increase in immunoreactive dyn-A-(1-17)-like material (irdyn-A). Estradiol (E2) replacement through sc SILASTIC implants for 1, 3, 7, and 14 days, which produces serum E2 levels between 25-35 pg/ml, restored in a time-dependent manner mRNA and peptide concentrations to values in sham-OVX rats. A significant decrease was observed after 3 days, and after 7 days, the effect was maximal. Tamoxifen (250 micrograms/kg.day, sc) administered simultaneously antagonized the action of E2 on Prodyn gene expression. Tamoxifen administered without E2 for 7 or 14 days significantly raised anterior pituitary levels of Prodyn mRNA and ir-dyn-A. To establish whether E2 and tamoxifen exert their effects on adenohypophyseal Prodyn mRNA by influencing the transcriptional activity of this gene, an in vitro transcriptional elongation assay was performed on nuclei from the anterior pituitary. The transcriptional rate of the Prodyn gene was significantly increased in 2-week OVX rats. Prodyn mRNA synthesis was suppressed in OVX rats exposed to E2, an effect antagonized by tamoxifen administered concomitantly. The antiestrogen administered alone for 14 days further elevated the transcriptional rate of Prodyn mRNA induced by gonadal ablation. In conclusion, E2 down-regulated the synthesis of Prodyn-derived peptides in adenohypophyseal cells. The antiestrogen tamoxifen antagonized the effect of E2 and, when chronically administered to OVX rats, further elevated the postcastrational rise in Prodyn gene expression.
强啡肽原（Prodyn）衍生肽在促性腺激素细胞的一个亚群中合成，并与促黄体生成素（LH）和促卵泡激素（FSH）同时释放，其在大鼠腺垂体中的水平受性腺类固醇环境的影响。在几个激素系统中，影响肽水平的因素可能会调节编码靶基因的信使核糖核酸（mRNA）的转录。因此，本研究旨在探讨性腺切除和雌激素替代对成年雌性大鼠垂体前叶Prodyn mRNA稳态水平变化及转录速率的影响。使用抗雌激素他莫昔芬进一步探究雌激素与强啡肽（dyn）相关肽之间的关系。采用溶液杂交-核糖核酸酶保护分析，在2周卵巢切除（OVX）大鼠中，Prodyn mRNA的稳态水平增加了一倍，同时免疫反应性强啡肽A-（1-17）样物质（irdyn-A）增加了3倍。通过皮下植入SILASTIC管1、3、7和14天进行雌二醇（E2）替代，使血清E2水平维持在25 - 35 pg/ml之间，可使mRNA和肽浓度以时间依赖性方式恢复到假手术OVX大鼠的水平。3天后观察到显著下降，7天后效果最佳。同时给予他莫昔芬（250微克/千克·天，皮下注射）可拮抗E2对Prodyn基因表达的作用。在无E2的情况下给予他莫昔芬7或14天可显著提高垂体前叶Prodyn mRNA和ir-dyn-A的水平。为确定E2和他莫昔芬是否通过影响该基因的转录活性对腺垂体Prodyn mRNA发挥作用，对垂体前叶细胞核进行了体外转录延伸分析。Prodyn基因的转录速率在2周OVX大鼠中显著增加。在暴露于E2的OVX大鼠中，Prodyn mRNA合成受到抑制，同时给予他莫昔芬可拮抗这一作用。单独给予抗雌激素14天可进一步提高性腺切除诱导的Prodyn mRNA转录速率。总之，E2下调了腺垂体细胞中强啡肽原衍生肽的合成。抗雌激素他莫昔芬拮抗E2的作用，并且当长期给予OVX大鼠时，可进一步提高去势后Prodyn基因表达的升高。
